"Over the past year, some of the leaders of the Republican Party in the Senate have done everything in their power to dry up my fundraising. The simple fact is that I have not raised the funds necessary to run an effective campaign for the U.S. Senate," Bunning said in a statement on his Web site.
Bunning, a Hall of Fame pitcher with the Detroit Tigers, Los Angeles Dodgers and Philadelphia Phillies, served in the House 1987-1999. He won close races in 1998 and 2004 to the Senate.
Bunning said his decision not to seek a third term was difficult "because I feel like my work in the Senate is more important now than ever."
He said he would finish out his term as a "strong voice against the domestic policies pushed by the White House and Congress that, if enacted, will put this country on the path to socialism."
Bunning is the sixth Republican Senator to announce plans not to seek re-election in 2010, The Washington Post reported. He joins Sens. Kit Bond of Missouri, Judd Gregg of New Hampshire, Sam Brownback of Kansas, George Voinovich of Ohio and Mel Martinez of Florida.